$\begin{array}{|l|l|l|}
\hline & \begin{array}{l}
\text{Number of unpaired e}
\end{array} & \mu=\sqrt{\mathrm{n}(\mathrm{n}+2)} B.M. \
\hline\left[\mathrm{Co}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+} & 3 & 3.87 \
\hline\left[\mathrm{Fe}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+} & 4 & 4.89 \
\hline\left[\mathrm{Mn}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+} & 5 & 5.92 \
\hline\left[\mathrm{Cr}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+} & 4 & 4.89 \
\hline
\end{array}Leastparamagneticbehaviour=\left[\mathrm{Co}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+}$